Re: [PATCH v1 03/11] perf: Allow for multiple ring buffers per event

Andi Kleen
2014-03-14T14:13:30Z

> > The other big problem is scalability. Even if it was somehow possible
> > to make this scheme work the IPIs for flushing would kill performance
> > on any multi threaded client. Given perf is not multi-threaded today, but
> > it doesn't seem a good idea to design the interface assuming no client ever
> > will be.
>
> Well any mmap()ed interface that wants to swap buffers will have this
> same problem.

There's no need to swap buffers in a sane design. The perf ring buffer
or the ftrace buffer don't need this. There's no need for a PT buffer
to do so either.

>
> You can restrict the TLB flushing to the threads that poll() on the
> relevant events. This just means other threads will see old/partial
> data, but that shouldn't be a problem as they shouldn't be looking in
> the first place.

Then we get incoherent processes. You're not serious about that are you?

-Andi

--
ak@linux.intel.com -- Speaking for myself only